workqueue: Automatically mark CPU-hogging work items CPU_INTENSIVE
If a per-cpu work item hogs the CPU, it can prevent other work items from
starting through concurrency management. A per-cpu workqueue which intends
to host such CPU-hogging work items can choose to not participate in
concurrency management by setting %WQ_CPU_INTENSIVE; however, this can be
error-prone and difficult to debug when missed.
This patch adds an automatic CPU usage based detection. If a
concurrency-managed work item consumes more CPU time than the threshold (5ms
by default), it's marked CPU_INTENSIVE automatically on schedule-out.
The mechanism isn't foolproof in that the 5ms detection delays can add up if
many CPU-hogging work items are queued at the same time. However, in such
situations, the bigger problem likely is the CPU being saturated with
per-cpu work items and the solution would be making them UNBOUND.
For occasional CPU hogging, the new automatic mechanism should provide
reasonable protection with minimal increase in code complexity.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
2 files changed
